BRL,
When you delete your Recycle Bin, it removes the pointers to all the files you had in the Recycle Bin. As long as Windows does not write over the location where the files were, they can be recovered, in pretty much the same way it was done in the days of DOS.
Take Care,
Richard
P.S. If you want to permanently remove data from your hard drive, you need to fill your hard drive with new data, use a magnet, or destroy the plates. Destroying the plates is the only guaranteed way your data will be destroyed.